html,body,h1,h2,h3,div,ul,li,p,a,img ,input,form {
    padding: 0;
    margin: 0;
    /* 设置和模型 */
    box-sizing: border-box; 
}
body {
    font-family: "微软雅黑",sans-serif;
    font-size: 13px;
    background: #eee;
}
a,
a:hover {
    color: #666;
    text-decoration: none;
}
ul {
    list-style: none;
}
input { 
    outline: none;
    border: none;
    border: 1px solid #ccc;
}
.fl {
    float: left;
}
.fr {
    float: right;
}
.clearfix::after { /*伪元素规范为::after*/
    content: '';
    display: block;
    clear: both;
    height: 0;
    overflow: hidden;
}